Make code style more consistent.

	modified:   README.md
	modified:   Rakefile
	modified:   bin/mdisc
	modified:   lib/mdisc.rb
	modified:   lib/mdisc/api.rb
	modified:   lib/mdisc/menu.rb
	modified:   lib/mdisc/player.rb
	modified:   lib/mdisc/ui.rb
	modified:   mdisc.gemspec